To be perfectly honest, I think widespread "legal marriage" that we know today (whether through the state or through the church) developed simply as a means of record keeping.<quoted text>
Nice try. Individual couples who cannot or choose not, to bear children, don't invalidate the premise as a whole. Do you have an alternative theory as to why marriage developed, and there's not a cross cultural cross time sustained ssm structure with deep seated roots?
Keep in mind that homosapien is believed to have been on the planet at least 100,000 years.
Imagine how it must have been in ancient, rural or sparsely populated areas of the world. Were there churches? Were there official governments?
My guess is that ancient people paired up and started families without the use of pastors or leaders or officials of any kind.
Widespread marriage came about much later.
I'm guessing... I have no proof.